calling the function before overridden in typescript produces a compiler error

zk.afterLoad('za11y, zkmax.layout', function() {
    const exWidget = zk.augment(zkmax.layout.Portallayout.prototype, {
        doKeyDown_: function () {
            // to skip the function in za11y, call its parent's parent's method
            exWidget.doKeyDown_.apply(arguments);
        },
    });
});

widgetCustomization/portallayout-disable-nav.ts:9:22 - error TS2339: Property 'doKeyDown_' does not exist on type 'Pick<Widget<any>, never>'.

9             exWidget.doKeyDown_.apply(arguments);
                       ~~~~~~~~~~